Bar code readers are found in many commercial environments such as, for example, point-of-sale stations in retail stores and supermarkets, inventory and document tracking, and diverse data control applications. To meet the growing demands, bar code symbol readers of various types have been developed for scanning and decoding bar code symbol patterns and producing symbol character data for use as input in automated data processing systems. The bar code scanners generally are available in hand-held, hands-free or in-counter formats.
In additions to on/off modes, many bar code scanners have a standby or sleep mode to conserve power. There are a variety of ways for a scanner to enter a sleep mode, for example, if scanned bar code data is not detected for a defined period of time, the scanner may enter the reduced power standby or sleep mode.
Once a scanner goes in to a sleep mode, it has to “wake up” to be operational again. A variety of methods for waking up bar code scanners are known in the art. One method uses a trigger mechanism. Some trigger mechanisms are mechanical switches that must be depressed or pushed to wake up the scanner. Some trigger mechanisms are capacitance touch plates. Using a switch or a capacitance touch plate to wake up a scanner exposes the sensitive electrical circuitry inside the scanners at risk from damage by electrostatic discharge (ESD). ESD is a sudden and momentary electric current that occurs when excess electric charge, stored on an electrically insulated body, finds a path to an object having a different electric potential. ESD can have a significant detrimental effect on electronic circuits, such as those inside bar code scanners.
In conventional bar code scanners, hand held and in-counter, infrared (IR) activation sensors are generally used for waking up the scanner. IR activation sensors have been commonly used in conventional in-counter bar code scanners. In an IR activation system, an IR detection unit constantly scans for a motion within a specific range in front of the scanning device. If a predetermined amount of motion or IR signal is detected by the IR detection unit, then the scanner is waken up. But because IR detection unit is an active device that is constantly on while the scanner is in the sleep mode, this solution diminishes the power-saving benefit of the sleep mode.
Yet another method of waking up a scanner is by intermittently turning on the bar code scanning circuitry of the scanner. In this method, the bar code scanning circuitry (e.g., the light source, oscillating mirror assembly and accompanying electrical circuitry, for example,) is pulsed on and off at a predetermined interval. If a usable data signal is returned, for example, a reflected light signal containing bar code information, then the scanner will exit the standby or sleep mode and remain on. In addition to consuming power by constantly turning the scanning circuitry on and off this method reduces the reliability of the scanner by continuously cycling the scanning circuitry and the associated mechanisms through on/off cycles when the scanner is in the sleep mode.
Thus, an improved method for waking up bar code scanners from sleep mode is desired.